"Attacks usually occur over weekends in order to maximise the amount of time the breaches will go unnoticed," Clifford said. "By the time business owners return to the office on Monday or after a long weekend, the damage has already been done."

"International criminals will scan business phone systems around the world in order to identify vulnerabilities which will make them easier to access. Once access is gained, criminals will log thousands of international calls to premium numbers — which in many cases they own — making a huge profit."

He said that many Perth businesses have "extremely vulnerable" VoIP networks and use "only the most basic security in place such as factory default access pins or passwords".

According to the Police, it's difficult to identify and prosecute VoIP fraudsters.

Neural Networks managing director Richard Stephens, who has fought VoIP attacks, said that passwords and prefixes should be enforced so that they cannot be easily guessed. He recommended other methods to prevent or reduce damage from VoIP attacks including placing caps on the amount of calls customers can make over a period, preventing calls being made to countries not usually contacted, and implementing systems to detect anomalous behaviour.

Darren Pauli has been writing about technology for almost five years, he covers a gamut of news with a special focus on security, keeping readers informed about the world of cyber criminals and the safety measures needed to thwart them.